1. Field of the Invention
The present invention relates to an image processing apparatus and an image taking apparatus such as a digital camera which improves image taking accuracy by correcting image blur caused by vibration and a program which is used for the apparatuses.
2. Description of Related Art
Operations important for image taking such as exposure determination and focusing, etc., of cameras that are currently used, have been completely automated, and even a person who is unskilled in camera operations is unlikely to cause an image taking failure.
Furthermore, recently, a system that represses image blur from being caused by vibration applied to the camera has also been studied, and factors that cause a photographer to fail in image taking have been reduced to almost zero.
Herein, a vibration isolation system that represses image blur is briefly described.
Camera shake when image taking appears as vibration with a frequency of, normally, 1 Hz through 10 Hz, and for enabling the camera to take a picture without image blur even when such vibration occurs at a point of exposure, it is required that camera shake due to vibration is detected and a correcting lens is displaced within an optical axis orthogonal plane according to the results of this detection (optical vibration isolation system).
Namely, in order to take a picture without image blur even when camera shake occurs, it becomes necessary that, first, camera shake is accurately detected, and second, an optical axis change due to vibration is corrected.
Camera shake can be detected by, in principle, mounting on a camera a vibration detecting unit that detects acceleration, angular acceleration, angular velocity, and angular displacement by means of a laser gyro, etc., and carries out appropriate calculation for the results of this detection. Then, by driving a correcting optical unit that makes an image taking optical axis eccentric on the basis of the detection information on camera shake outputted from the vibration detecting unit, image blur correction is carried out.
On the other hand, Japanese Patent Publication No. 3110797 discloses a method in which image taking is repeated a plurality of times in an exposure period with a length that does not cause vibration, and a plurality of images obtained through the image taking are synthesized while correcting image divergence among the images to obtain a taken image (synthesized image) of a long exposure period.
Recent digital cameras have become smaller in size than silver haloid compact cameras, and in particular, a camera that has an image pickup device of a VGA class has been downsized so that it is built-in a portable electronics device (such as a portable phone). In order to mount the abovementioned optical vibration isolation system on a camera, it is necessary that the vibration correcting optical unit is made smaller or the vibration detecting unit is made smaller.
However, in the vibration correcting optical unit, since a correcting lens must be supported and highly accurately driven, there is a limit to downsizing. In addition, most of the vibration detecting units that are currently used utilize inertia, so that if the vibration detecting units are downsized, detection sensitivity lowers and accurate vibration correction becomes impossible.
Furthermore, vibration to be applied to cameras includes angular vibration around a predetermined axis and shifting vibration that shakes a camera parallel, and although the angular vibration is correctable by the optical vibration isolation system, the shifting vibration is hardly corrected. This shifting vibration tends to become greater as the camera becomes smaller.
On the other hand, as a different vibration isolation system, as employed in a video camera for taking a moving image, a method in which a motion vector of an image plane is detected based on an output of an image pickup device and an image readout position is changed according to the detected motion vector to obtain a moving image without image blur can also be employed. This method has an advantage in that the camera can be downsized since the vibration detecting unit and the correcting lens in the abovementioned optical vibration isolation system become unnecessary.
However, this vibration isolation system used in video cameras cannot be easily applied to digital cameras. The reason for this is described below.
Motion vector extraction in a video camera is carried out for each image reading, and for example, when images of 15 frames are extracted per second, a motion vector is detected by comparing these extracted images.
However, in a case where a still image is taken by a digital camera, exposure is carried out only once for an object to be taken, so that motion vector detection through comparison of images as in a video camera is not possible. Therefore, the vibration isolation system for video cameras cannot be simply applied to digital cameras.
On the other hand, in the vibration isolation method disclosed in Japanese Patent Publication No. 3110797, since image taking is repeated a plurality of times, an image taking period becomes long. The long image taking period does not pose a problem when an image of a still object is taken. However, when an image of an object such as a person that even slightly moves is taken, shake of an object side (object vibration) is caused, and image blur caused by object vibration cannot be suppressed although image blur caused by hand vibration can be suppressed, and a taken image may deteriorate.